Various circumstances require that exposure to certain environmental factors, such as heat and ultraviolet (UV) light be monitored and recorded. For example, the need to know whether a product has been exposed either to an undesirable time-temperature history, which results in substantial degradation, or to a correct time-temperature history required during processing is frequently required. This applies, for example, to frozen foods, pharmaceuticals or photographic films that may be exposed to undesirable high temperatures for significant time periods during storage and distribution. Additionally, exposure to the ultraviolet radiation of sunlight can cause rapid aging and hardening of the skin and can cause DNA damage, which can lead to skin cancer or other cellular proliferative diseases.
Diacetylenes are typically colorless and undergo addition polymerization, either thermally or by actinic radiation. As the polymerization proceeds, these compounds undergo a contrasting color change to blue or purple. Utilization of this class of compounds is known for use as time-temperature history indicators, thermochromic indicating materials and as radiation-dosage indicators.
Efforts continue, however, to make sensing devices employing diacetylenes more accurate, more tailored to a given application, less complex and more available to non-technical personnel in a wide variety of environments. Devices, which can be conveniently transported and used individually for a particular application then discarded, are particularly desirable.